A configuration example of an optical duplexer is known from DE 42 30 952 A1, in which a silicon substrate equipped with integrated optical functional units is affixed in a housing, among others. The silicon substrate supports a beam splitter, which is integrated in the form of optical line paths and acts as a directionally selective wavelength coupler. A semiconductor laser diode is coupled before one end of a first straight line path, and a fiber optic pigtail is coupled to the other end of this line path. A second optical line path, which is coupled to the first line path by a cut that runs parallel to it, ends in a bent cut before a photodiode which is affixed to the silicon substrate.